The age of striatum determines the pattern and extent of dopaminergic innervation: A nigrostriatal double graft study

GDNF is important for striatal organization and maintenance of dopamine neurons grown in the presence of the striatum

Glial cell line-derived neurotrophic factor (GDNF) exerts neuroprotective and neurorestorative effects on neurons and GDNF plays a significant role in maintenance of the dopamine neurons utilizing grafting to create a nigrostriatal microcircuit of Gdnf knockout (Gdnf(-/-)) tissue. To further evaluate the role of GDNF on organization of the nigrostriatal system, single or double grafts of ventral mesencephalon (VM) and lateral ganglionic eminence (LGE) with mismatches in Gdnf genotypes were performed. The survival of single grafts was monitored utilizing magnetic resonance imaging (MRI) and cell survival and graft organization were evaluated with immunohistochemistry. The results revealed that the size of VM single grafts did not change over time independent of genotype, while the size of the LGE transplants was significantly reduced already at 2 weeks postgrafting when lacking GDNF. Lack of GDNF did not significantly affect the survival of tyrosine hydroxylase (TH)-positive neurons in single VM grafts. However, the survival of TH-positive neurons was significantly reduced in VM derived from Gdnf(+/+) when co-grafted with LGE from the Gdnf(-/-) tissue. In contrast, lack of GDNF in the VM portion of co-grafts had no effect on the survival of TH-positive neurons when co-grafted with LGE from Gdnf(+/+) mice. The TH-positive innervation of co-grafts was sparse when the striatal co-grafts were derived from the Gdnf(-/-) tissue while dense and patchy when innervating LGE producing GDNF. The TH-positive innervation overlapped with the organization of dopamine and cyclic AMP-regulated phosphoprotein-relative molecular mass 32,000 (DARPP-32)-positive neurons, that was disorganized in LGE lacking GDNF production. In conclusion, GDNF is important for a proper striatal organization and for survival of TH-positive neurons in the presence of the striatal tissue.

Glial cell line-derived neurotrophic factor is crucial for long-term maintenance of the nigrostriatal system

Glial cell line-derived neurotrophic factor (GDNF) is a potent factor for the ventral mesencephalic dopamine neurons. However, studies on the Gdnf gene deleted (Gdnf(-/-)) mouse have been limited to fetal tissue since these mice die prematurely. To evaluate long-term effects of Gdnf gene deletion, this study involves co-grafts of ventral mesencephalon (VM) and lateral ganglionic eminence (LGE) derived from different Gdnf genotypes. The VM/LGE co-grafts were evaluated at 3, 6, and 12 months for tyrosine hydroxylase (TH) -positive cell survival and nerve fiber formation in the LGE co-transplant, visualized by dopamine- and cyclic AMP-regulated phosphoprotein relative molecular mass 32,000 (DARPP-32) -immunoreactivity. Cell counts revealed no difference in TH-positive neurons between Gdnf genotypes at 3 months postgrafting. At 6 months, a significant reduction in cell number was observed in the Gdnf(-/-) grafts. In fact, in the majority of the Gdnf(-/-) VM/LGE transplant had degenerated. At 12 months, a reduction in cell number was seen in both Gdnf(-/-) and Gdnf(+/-) compared to wild type transplants. In the Gdnf(-/-) grafts, TH-negative inclusion-like structures were present in the cytoplasm of the TH-positive neurons at 3 months. These structures were also found in the Gdnf(+/-) transplants at 12 months, but not in Gdnf(+/+) controls at any time point. In Gdnf(+/+) grafts, TH-positive nerve fiber innervation of the striatal co-grafts was dense and patchy and overlapped with clusters of DARPP-32-positive neurons. This overlap did mismatch in the Gdnf(+/-) grafts, while the TH-positive innervation was sparse in the Gdnf(-/-) transplants and the DARPP-32-positive neurons were widespread distributed. In conclusion, GDNF is essential for long-term maintenance of both the VM TH-positive neurons and for the striatal tissue, and appears crucial for generation of a proper organization of the striatum.

Making connections: the development of mesencephalic dopaminergic neurons

The disorders of two adjacent sets of mesencephalic dopaminergic (MDNs) are associated with two significant health problems: Parkinson's disease and drug addiction. Because of this, a great deal of research has focused on understanding the growth, development and maintenance of MDNs. Many transcription factors and signaling pathways are known to be required for normal MDNs formation, but a unified model of MDN development is still unclear. The long-term goal is to design therapeutic strategies to: (i) nurture and/or heal endogenous MDNs, (ii) replace the affected tissue with exogenous MDNs from in vitro cultivated stem cells and (iii) restore normal connectivity. Recent developmental biology studies show great promise in understanding how MDNs develop both in vivo and in vitro. This information has great therapeutic value and may provide insight into how environmental and genetic factors increase vulnerability to addiction.

Guidance of dopaminergic neuritic growth by immature astrocytes in organotypic cultures of rat fetal ventral mesencephalon

Astrocytes, with their many functions in producing and controlling the environment in the brain, are of great interest when it comes to studying regeneration after injury and neurodegenerative diseases such as in grafting in Parkinson's disease. This study was performed to investigate astrocytic guidance of growth derived from dopaminergic neurons using organotypic cultures of rat fetal ventral mesencephalon. Primary cultures were studied at different time points starting from 3 days up to 28 days. Cultures were treated with either interleukin-1 beta (IL-1 beta), which has stimulating effects on astrocytic proliferation, or the astrocytic inhibitor cytosine arabinoside (Ara-C). Tyrosine hydroxylase (TH)-immunohistochemistry was used to visualize dopaminergic neurons, and antibodies against glial fibrillary acidic protein (GFAP) and S100 beta were used to label astrocytes. The results revealed that a robust TH-positive nerve fiber production was seen already at 3 days in vitro. These neurites had disappeared by 5 days. This early nerve fiber outgrowth was not guided by direct interactions with glial cells. Later, at 7 days in vitro, a second wave of TH-positive neuritic outgrowth was clearly observed. GFAP-positive astrocytic processes guided these neurites. TH-positive neurites arborized overlying S100 beta-positive astrocytes in an area distal to the GFAP-positive astrocytic processes. Treatment with IL-1 beta resulted in an increased area of TH-positive nerve fiber network. In cultures treated with Ara-C, neither astrocytes nor outgrowth of dopaminergic neurites were observed. In conclusion, this study shows that astrocytes play a major role in long-term dopaminergic outgrowth, both in axonal elongation and branching of neurites. The long-term nerve fiber growth is preceded by an early transient outgrowth of dopamine neurites.

Evidence for Target-Specific Nerve Fiber Outgrowth from Subpopulations of Grafted Dopaminergic Neurons: A Retrograde Tracing Study Using in Oculo and Intracranial Grafting

Efforts have been made to counteract the symptoms of Parkinson's disease by substituting the loss of dopaminergic neurons with fetal ventral mesencephalic grafts. One of the postulated limiting factors in this treatment is the relatively poor cell survival and limited graft-derived fiber outgrowth. Recent results documenting enhanced survival of grafted dopaminergic neurons showed no positive correlation to enhanced innervation of the striatal target. Therefore this study was undertaken to investigate whether all surviving grafted dopaminergic neurons projected to the striatal target. Hence, fetal ventral mesencephalic tissue was implanted adjacent to mature versus immature striatal tissue using in oculo and intraventricular grafting techniques. In in oculo grafting, fetal ventral mesencephalon was implanted simultaneously with fetal lateral ganglionic eminence (immature striatal target) or to already matured striatal in oculo grafts (mature striatal target). Furthermore, fetal ventral mesencephalon was implanted into the lateral ventricle adjacent to mature dopamine-depleted striatum. The retrograde tracer fluorogold was injected into the striatal portion of the in oculo cografts and into reinnervated areas of the adult brain. Immunohistochemistry revealed that a significantly larger proportion of tyrosine hydroxylase-positive neurons in the ventral mesencephalic graft was innervating in oculo immature striatal tissue, and hence was fluorogold-positive, in comparison with the number of tyrosine hydroxylase-positive neurons innervating mature striatal tissue. Moreover, intracranial transplantations showed that tyrosine hydroxylase-positive neurons were distributed within the grafts in dense clusters of cells. In most clusters tyrosine hydroxylase-positive cells were fluorogold-negative but calbindin-positive. In a few tyrosine hydroxylase-positive cell clusters, neurons were coexpressing fluorogold but were calbindin-negative. In conclusion, significantly more dopamine neurons projected to immature than to mature striatal tissue and thus, a subpopulation of grafted dopaminergic neurons was not projecting into adult striatum. Thus, the results from this study show that further attempts to enhance survival of grafted dopamine neurons in purpose to enhance graft-derived fiber outgrowth and efficacy should also consider different subtypes of dopamine neurons.

Implantation of bioactive growth factor-secreting rods enhances fetal dopaminergic graft survival, outgrowth density, and functional recovery in a rat model of Parkinson's disease

One of the drawbacks with fetal ventral mesencephalic (VM) grafts in Parkinson's disease is the limited outgrowth into the host striatum. In order to enhance graft outgrowth, epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) were administered by implantation of bioactive rods to the lateral part of the striatum to support grafted fetal VM implanted to the medial portion of the striatum. The polymer-based bioactive rods allow for a local secretion of neurotrophic factors over a time period of approximately 2 weeks. Moreover, glial cell line-derived neurotrophic factor (GDNF) and transforming growth factor-beta1 (TGFbeta1) were administered using the same technique. Concomitant administration of GDNF and TGFbeta1 was achieved by insertion of one GDNF and one TGFbeta1 rod. This was performed to investigate possible additive effects between GDNF and TGFbeta1. Rotational behavior, outgrowth from and nerve fiber density within the VM graft, and the number of TH-positive cells were studied. Functional compensation by reduction of rotational behavior was significantly enhanced in animals carrying bFGF and GDNF rods in comparison with animals carrying only VM graft. EGF and bFGF significantly increased the innervation density. Moreover, the nerve fiber density within the grafts was significantly enhanced by bFGF. Cell counts showed that a significantly higher number of TH-positive neurons was found in grafts treated with bFGF than that found in GDNF-treated grafts. An additive effect of TGFbeta1 and GDNF was not detectable. These results suggest that bioactive rods is a useful tool to deliver neurotrophic factors into the brain, and since bFGF was a potent factor concerning both functional, immunohistochemical and cell survival results, it might be of interest to use bFGF-secreting rods for enhancing the overall outcome of VM grafts into patients suffering from Parkinson's disease.

Tirilazad mesylate increases dopaminergic neuronal survival in the in Oculo grafting model

Grafting of fetal ventral mesencephalon in Parkinson's disease has been extensively studied. A crucial draw back of this technique is the low survival rate of the dopaminergic neurons. It has been documented that only 5-20% of the grafted neurons survive, and to enhance graft efficacy to a satisfying level, increased cell survival is of utmost desire. In this study we have used the antioxidant tiriliazad mesylate (U-74006F) to study the effect on the survival of dopaminergic neurons after grafting. The in oculo grafting model was used and ventral mesencephalon was dissected from E14-E15 rat fetuses in Hanks' balanced salt solution (HBSS), in Dulbecco's modified Eagle medium (DMEM), or in 0.3, 3.0, or 30 microM U-74006F diluted in DMEM. The tissue was then inserted into the anterior chamber of the eye. Some of the transplants were further treated with intraocular injections of 3 or 30 microM U-74006F (5 microliters) weekly for 2 weeks. Quantification of tyrosine hydroxylase (TH)-immunoreactive profiles revealed that in transplants treated with U-74006F at dissection only, no change in the number of TH-positive neurons was found. Pretreatment of 0.3 microM U-74006F during dissection combined with intraocular injections of U-74006F after grafting, on the other hand, resulted in a dose-dependent enhancement of survival of TH-positive neurons. Dissection in, and intraocular treatment with, 3 microM U-74006F resulted in a significantly enhanced survival of TH-positive neurons whereas using U-74006F at a concentration of 30 microM did not change the cell survival compared to solely DMEM-treated grafts. Thus, 30 microM was interpreted to be an overdose. Comparing cell survival when dissected in DMEM with that dissected in HBSS showed that DMEM was clearly superior. Nerve fiber formation was most pronounced in grafts treated with 3 microM U-74006F. In conclusion, survival of TH-positive neurons is enhanced by U-74006F, which is readily available for clinical use and thus could be employed to enhance graft survival when transplanting patients suffering from Parkinson's disease.